%>  lines from FILE2
    %=  lines common to FILE1 and FILE2
    %[-][WIDTH][.[PREC]]{doxX}LETTER  printf-style spec for LETTER
      LETTERs are as follows for new group, lower case for old group:
        F  first line number
        L  last line number
        N  number of lines = L-F+1
        E  F-1
        M  L+1
    %(A=B?T:E)  if A equals B then T else E